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Old 07-16-2011, 05:34 PM   #1
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Can a takeoff be installed out of the top of the plenum?


Recently purchased a house that was added onto a few years back.The new addition cools just fine but the original structure is at least 6 degrees warmer.Was wondering if I could add another duct from the top of the plenum as all four sides are being used?If not, then how could I go about resolving this isssue?Thanks

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Old 07-16-2011, 05:42 PM   #2
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Can a takeoff be installed out of the top of the plenum?


To add another duct, you need to increase your AC tonnage......to get this right, you need to redo all load calculation etc. Is not just add more ducts.

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Old 07-16-2011, 06:19 PM   #3
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Can a takeoff be installed out of the top of the plenum?


Could try increasing the fan speed, it may not have been set for max speed when they installed the furnace.
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Old 07-16-2011, 09:23 PM   #4
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Can a takeoff be installed out of the top of the plenum?


It sounds as if you've already done the work if the rest of the home is all of a sudden 6 degrees warmer. Oops.

Static pressure is the issue when dealing with plenums. If you open up the rear by adding a duct and especially a bigger sized one you lose pressure everywhere else as the air flows to the easiest path possible, in this case straight out the back. The only excpetion I'll personally make when I have no other absolute choice is if it's a 4" or 5" duct to a very small room such as a restroom and even then if the air flow remains good throughout the home I still don't like. And I always put it in a corner, not the middle.

You should stay 6" from the top or end cap rather and 6" in from the side that attaches to the evaporator coil for best results (scientifically speaking) and duct takoffs should be criss crossed from one another so not directly opposing.

Not mandatory but good practice, the latter sentence.

Good luck.

Last edited by Doc Holliday; 07-16-2011 at 09:28 PM.
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Old 07-17-2011, 06:59 AM   #5
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Can a takeoff be installed out of the top of the plenum?


I would cut back on the airflow to the new addition and see if I could add More air to the existing and I would check my returns, got to have adequate return air also

Oh check thermostat location also. So many things to check.

Last edited by COLDIRON; 07-17-2011 at 07:00 AM. Reason: changed
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Old 07-17-2011, 07:16 AM   #6
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Can a takeoff be installed out of the top of the plenum?


Quote:
Originally Posted by COLDIRON View Post
I would cut back on the airflow to the new addition and see if I could add More air to the existing and I would check my returns, got to have adequate return air also

Oh check thermostat location also. So many things to check.
yep, damper back the addition.

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